Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755254Ab3H1LQu (ORCPT ); Wed, 28 Aug 2013 07:16:50 -0400 Received: from merlin.infradead.org ([205.233.59.134]:60768 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754076Ab3H1LQt (ORCPT ); Wed, 28 Aug 2013 07:16:49 -0400 Date: Wed, 28 Aug 2013 13:16:38 +0200 From: Peter Zijlstra To: Ingo Molnar , Joonsoo Kim Cc: linux-kernel@vger.kernel.org, Mike Galbraith , Paul Turner , Alex Shi , Preeti U Murthy , Vincent Guittot , Morten Rasmussen , Namhyung Kim , Lei Wen , Joonsoo Kim , Rik van Riel Subject: [RFC][PATCH 14/10] sched, fair: Fix the group_capacity computation Message-ID: <20130828111638.GO10002@twins.programming.kicks-ass.net> References: <20130819160058.539049611@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130819160058.539049611@infradead.org> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2198 Lines: 59 Subject: sched, fair: Fix the group_capacity computation From: Peter Zijlstra Date: Wed Aug 28 12:40:38 CEST 2013 Do away with 'phantom' cores due to N*frac(smt_power) >= 1 by limiting the capacity to the actual number of cores. The assumption of 1 < smt_power < 2 is an actual requirement because of what SMT is so this should work regardless of the SMT implementation. It can still be defeated by creative use of cpu hotplug, but if you're one of those freaks, you get to live with it. Signed-off-by: Peter Zijlstra --- kernel/sched/fair.c | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-) --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4554,18 +4554,24 @@ static inline int sg_imbalanced(struct s /* * Compute the group capacity. * - * For now the capacity is simply the number of power units in the group_power. - * A power unit represents a full core. - * - * This has an issue where N*frac(smt_power) >= 1, in that case we'll see extra - * 'cores' that aren't actually there. + * Avoid the issue where N*frac(smt_power) >= 1 creates 'phantom' cores by + * first dividing out the smt factor and computing the actual number of cores + * and limit power unit capacity with that. */ static inline int sg_capacity(struct lb_env *env, struct sched_group *group) { + unsigned int capacity, smt, cpus; + unsigned int power, power_orig; + + power = group->sgp->power; + power_orig = group->sgp->power_orig; + cpus = group->group_weight; - unsigned int power = group->sgp->power; - unsigned int capacity = DIV_ROUND_CLOSEST(power, SCHED_POWER_SCALE); + /* smt := ceil(cpus / power), assumes: 1 < smt_power < 2 */ + smt = DIV_ROUND_UP(SCHED_POWER_SCALE * cpus, power_orig); + capacity = cpus / smt; /* cores */ + capacity = min_t(capacity, DIV_ROUND_CLOSEST(power, SCHED_POWER_SCALE)); if (!capacity) capacity = fix_small_capacity(env->sd, group); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/